1. Technical Field
The invention is related InGaAs photodetectors and in particular to a monolithic InGaAs focal plane array detector responsive to light in the visible and short wavelength infrared wavelength range.
2. Background Art
InGaAs detectors enjoy a dual advantage of being able to operate at relatively high temperatures and of being able to detect short wavelength infrared light as well as visible light. Typically, InGaAs imagers assume a hybrid structure in which the InGaAs photodetector array is indium-bump bonded to an underlying substrate (e.g., silicon) containing the readout electronics.
An exciting prospect offered by the present invention in the development of InGaAs infrared detectors is the possibility of fabricating a truly monolithic short wavelength infrared focal plane array with high detectivity. Integration of the readout with the photodetector has worked in silicon, but attempts at monolithic mercury cadmium telluride focal plane arrays have met with limited success at best. A monolithic focal plane array has several advantages over hybrid structures. The focal plane size is not limited by thermal matching considerations, so that very large sensors, such as those realized in monolithic silicon CCDs, are possible. If a monolithic InGaAs focal plane array can be made (as in the present invention), then the indium bump process and associated hybrid structure is eliminated.
A further advantage is that a truly monolithic InGaAs focal plane would have immediate wide usage and application based upon the enormous growth and investment of the optoelectronics integrated circuit industry in InGaAs technology. The demand for InGaAs diode lasers, high speed detectors and light modulators for fiber optic communications in the 1.3-1.66 micron range has grown in recognition of the advantages of InGaAs over other semiconductors.
A further advantage is that the manufacturability of InGaAs infrared focal plane array is much greater than that of equivalent mercury cadmium telluride arrays, due to several factors: (a) the advanced state of growth techniques for III-V compound semiconductors, including molecular beam epitaxy, metal-organic chemical vapor deposition, liquid phase epitaxy, hydride-transport vapor phase epitaxy and atomic layer epitaxy. Another advantage is the higher quality of III-V compound semiconductor substrates and their more rugged nature, tending to lead to processing yield increases over II-VI compound semiconductors.
However, monolithic InGaAs focal plane arrays are not generally known in the art. One related structure is an optical pulse detector disclosed in U.S. Pat. No. 4,904,607 to Riglet et al. This patent discloses a monolithic integrated circuit containing an InGaAs photodetector and output circuitry consisting of InGaAs junction field effect transistors (JFETs). The principal function of the JFET output circuitry is to widen the extremely narrow pulse produced by the photodetector upon receipt of an equally narrow optical pulse. In this process, the amplitude (photon flux) of the received optical pulse is not measured, and there is no integration of photon-generated carriers in the sense that a focal plane imager integrates photon-generated carriers during successive integration periods.
Thus, what is needed is a monolithic integrated indium (In)-based III-V compound semiconductor focal plane array including readout circuitry.